fix(server): skip embedding when not configured (#12544)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Bug Fixes**
  - Improved reliability by ensuring certain features are only enabled when required support and configuration are present, reducing the risk of runtime errors.
  - Enhanced platform detection logic for better accuracy across different environments, including macOS and Windows systems.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/context/job.ts

@@ -52,9 +52,11 @@ export class CopilotContextDocJob {
   private async setup() {
     this.supportEmbedding =
       await this.models.copilotContext.checkEmbeddingAvailable();
-    this.client = new OpenAIEmbeddingClient(
-      this.config.copilot.providers.openai
-    );
+    if (this.supportEmbedding && this.config.copilot.providers.openai.apiKey) {
+      this.client = new OpenAIEmbeddingClient(
+        this.config.copilot.providers.openai
+      );
+    }
   }
 
   // public this client to allow overriding in tests